1. Field of Invention
The present invention relates generally to fiber channel communications over dense wave division multiplexing (DWDM) networks. More particularly, the present invention relates to a system which enables distance extension, as well as other transport functions, to be efficiently achieved between a pair of fiber channel switches or nodes.
2. Description of the Related Art
Fiber channel is a protocol that is used extensively for storage networking, and allows data to be transmitted between computing systems at data rates of up to approximately ten Gigabits per second (Gbps). As will be appreciated by those skilled in the art, fiber channel uses a Gigabit Ethernet physical layer for transmission.
Fiber channel capabilities are typically such that between two fiber channel switches or nodes coupled to storage systems, a transmission distance of up to approximately ten kilometers may be achieved without compromising data throughput. As the use of networks increases, however, transmission distances that are significantly greater than ten kilometers are often desired, particularly when a storage network is used to mirror data geographical locations. By way of example, transmission distances of between approximately 500 kilometers and approximately 1000 kilometers may be needed in storage networks which utilize fiber channel devices.
To achieve transmission distances that exceed the approximately ten kilometer transmission distances that are generally possible between two fiber channel nodes, distance extension techniques may be implemented. Incorporating fiber channel transport nodes with storage capabilities into a path between two fiber channel nodes, e.g., switches, provides the capability to achieve full data throughput over an extended distance.
Fiber channel transport nodes such as fiber channel transport linecards may be included in a path between fiber channel switches to provide distance extension. Such fiber channel transport linecards may include buffers to temporarily store fiber channel frames that are to be transported between two fiber channel clients. In order to establish flow control between two fiber channel transport linecards, buffer-to-buffer credit thresholds are effectively determined for each fiber channel transport linecard. A buffer-to-buffer credit threshold is an indicator of the total number of credits associated with the fiber channel device, or a substantially maximum number of frames a fiber channel transmit linecard may accept for storage and transmission without acknowledgement from receiver. The number of buffer-to-buffer credits associated with a fiber channel devices is dependent upon the distance over which the fiber channel device is expected to transmit frames. Hence, for a given path length, the throughput for the path is a function of the number of buffer-to-buffer credits available for the fiber channel transport linecards in the path.
As bandwidth is generally expensive, in order for fiber channel transport linecards to efficiently use bandwidth in a path, the fiber channel transport linecards generally must be made aware of the number of buffer-to-buffer credits associated with other fiber channel linecards. By way of example, a first fiber channel transport linecard, or a local linecard, must be aware of how many buffer-to-buffer credits are associated with a second fiber channel transport linecard, or remote linecard, if the first fiber channel transport linecard is to efficiently use available bandwidth on a link between the first fiber channel transport linecard and the second fiber channel transport linecard.
When a fiber channel frame is to be sent from a first fiber channel transport linecard to a second fiber channel transport linecard, the first fiber channel transport linecard may encapsulate the first fiber channel frame such that the fiber channel frame may be carried on a different protocol. The different protocols may include Gigabit Ethernet protocols, and Synchronous Optical Network (SONET) protocols such as OC-48 and OC-192.
After encapsulating the fiber channel frame, the first fiber channel transport linecard adds link management information, e.g., information about the buffer-to-buffer credits associated with the first fiber channel transport linecard, to the encapsulated fiber channel frame. Once the link management information is added to the encapsulated fiber channel frame, the encapsulated fiber channel frame is sent to the second fiber channel transport linecard which may then utilize the link management information.
Although the use of encapsulated fiber channel frames with link management information allows the link management information to be propagated from one fiber channel transport linecard to another, the encapsulation process is often complex and time consuming. Extra hardware resources may be necessary for encapsulation, thereby adding costs to an overall system. Further, the transmission of encapsulated fiber channel frames utilizes significant bandwidth, which is expensive, and is not protocol independent or scaleable.
Therefore, what is needed is an efficient method for providing distance extension for a fiber channel path. That is, what is desired is an efficient system which allows management information to be communicated between fiber channel transport linecards used for distance extension purposes without utilizing additional bandwidth.